1. Field of the Invention
The present invention relates to a solid-state image pick-up device comprising a plurality of photoelectric converting devices provided in a row direction and a column direction orthogonal thereto over the surface of a semiconductor substrate, and more particularly to a solid-state image pick-up device comprising a photoelectric converting device having a relatively high sensitivity and a photoelectric converting device having a relatively low sensitivity.
2. Description of the Related Art
A solid-state image pick-up device to be utilized in a digital camera detects a charge corresponding to an image signal by means of a photoelectric converting device. In general, therefore, it is hard to increase a dynamic range. Therefore, there has been employed a processing of continuously carrying out high-sensitivity image-capturing and low-sensitivity image-capturing in a short time and synthesizing two images thus acquired in order to obtain an image having a wide dynamic range. However, the two images to be synthesized are not obtained at the same time. For this reason, there is a problem in that an unnatural image is picked up if an object having a motion is photographed.
As another solving means, there is utilized a solid-state image pick-up device including a photoelectric converting device having a relatively high sensitivity (which will be hereinafter referred to as a “high-sensitivity pixel” in some cases) and a photoelectric converting device having a relatively low sensitivity (which will be hereinafter referred to as a “low-sensitivity pixel” in some cases). FIG. 3 is a view showing the schematic structure of a solid-state image pick-up device having a so-called honeycomb structure, that is, a solid-state image pick-up device comprising a photoelectric converting device having a high sensitivity and a photoelectric converting device having a low sensitivity.
The solid-state image pick-up device shown in FIG. 3 serves to convert a light intensity into a charge signal by a plurality of low-sensitivity pixels 10 and a plurality of high-sensitivity pixels 20, to transfer a signal charge to an output section 50 through a plurality of vertical transfer sections 30 (only a part thereof has the designation in FIG. 3) and a horizontal transfer section 40, and to output a voltage signal 51 corresponding to the signal charge from the output section 50.
The low-sensitivity pixel 10 and the high-sensitivity pixel 20 (only a part thereof has designations in FIG. 3) are arranged like a tetragonal grid in a row direction X and a column direction Y orthogonal thereto. The array pitch of the low-sensitivity pixel 10 is equal to that of the high-sensitivity pixel 20, and the low-sensitivity pixel 10 and the high-sensitivity pixel 20 are arranged in positions shifted by ½ of an array pitch from each other in the row direction X and the column direction Y. In order to change the sensitivity of the photoelectric converting device such as a photodiode constituting the low-sensitivity pixel 10 and the high-sensitivity pixel 20, the area of the light receiving plane of the photoelectric converting device may be varied or a collecting area may be varied by means of a microlens provided above the photoelectric converting device. Since all these methods are well-known, description will be omitted.
Moreover, the solid-state image pick-up device in FIG. 3 has a color filter (not shown) above the low-sensitivity pixel 10 and the high-sensitivity pixel 20 in order to detect a color image signal. While a method of arranging the color filter is optional, it is preferable that the array of the low-sensitivity pixel 10 should be identical to that of the high-sensitivity pixel 20 in order to obtain an image having a wide dynamic range. In FIG. 3, the color filter has a Bayer array and the corresponding photoelectric converting devices detect charges corresponding to red, green and blue lights, respectively. In some cases, signals corresponding to the red, green and blue lights which are detected by the high-sensitivity pixel 20 will be referred to as R, G and B signals (or simply R, G and B) and signals corresponding to the red, green and blue colors which are detected by the low-sensitivity pixel 10 will be referred to as r, g and b signals (or simply r, g and b).
The vertical transfer section 30 serves to transfer charges from the low-sensitivity pixel 10 and the high-sensitivity pixel 20 in the column direction Y and includes a plurality of vertical transfer channels (not shown) formed on a semiconductor substrate, a plurality of vertical transfer electrodes 101 to 104 formed to cross each of the vertical transfer channels as seen on a plane, and a charge reading region for reading the charges of the low-sensitivity pixel 10 and the high-sensitivity pixel 20 onto the vertical transfer channels (which are typically shown in an arrow of FIG. 3).
The vertical transfer channels take a winding shape extended wholly in the column direction Y between the low-sensitivity pixel 10 and the high-sensitivity pixel 20, and a region for storing and receiving the charge is partitioned by the vertical transfer electrodes 101 to 104 formed above the vertical transfer channels. The four vertical transfer electrodes 101 to 104 are provided corresponding to the low-sensitivity pixel 10 and the high-sensitivity pixel 20 respectively (any of them which corresponds to the high-sensitivity pixels for one row has the designation in the drawing) and take a winding shape extended wholly in the row direction X between the low-sensitivity pixel 10 and the high-sensitivity pixel 20. While the shapes of the region partition for storing and receiving the charges are connected in FIG. 3, the region is actually formed by conductors having almost equal widths.
Vertical transfer pulses having four phases are applied to the vertical transfer electrodes 101 to 104 through terminals 111 to 114 and the charges of the vertical transfer channels are transferred in the column direction Y. The vertical transfer pulse is also applied to transfer electrodes 105 and 106 between the vertical transfer section 30 and the horizontal transfer section 40, and the charges detected by the low-sensitivity pixel 10 and the high-sensitivity pixel 20 for one row are sent to the horizontal transfer section 40 every cycle of the vertical transfer pulse. The reading operation from the low-sensitivity pixel 10 and the high-sensitivity pixel 20 to the vertical transfer channel is carried out by superposing a reading pulse on a first phase pulse to be applied immediately after the start of vertical charge transfer (a vertical transfer pulse to be applied to the terminal 111) and a third phase pulse (a vertical transfer pulse to be applied to the terminal 113).
A channel stopper is formed between the vertical transfer channels, which is not shown in FIG. 3. Moreover, while the vertical transfer electrodes 101 to 104 are shown to be larger than the low-sensitivity pixel 10 and the high-sensitivity pixel 20 in FIG. 3, they are actually smaller.
The horizontal transfer section 40 serves to transfer a charge from the vertical transfer section 30 in the row direction X and includes a horizontal transfer channel and a horizontal transfer electrode (which are not shown). Horizontal transfer pulses having two phases are applied to the horizontal transfer electrode through terminals 121 and 122 and the signal charges of the low-sensitivity pixel 10 for one row and the high-sensitivity pixel 20 for one row which are sent from the vertical transfer section 30 are transferred to the output section 50.
Next, description will be given to the driving operation of the solid-state image pick-up device shown in FIG. 3. Charges stored in the low-sensitivity pixel 10 and the high-sensitivity pixel 20 corresponding to the intensity of a light incident from a field are read onto the vertical transfer channel in response to the reading pulse to be superposed on the first and third phase vertical transfer pulses. Then, the charges are transferred in the vertical transfer channel in response to the vertical transfer pulse and are held in the predetermined region of the horizontal transfer channel. Subsequently, when the horizontal transfer pulse is applied, the held charges are sequentially sent to the output section 50 and the voltage signal 51 corresponding to the amount of the charges is output.
As described above, in the conventional solid-state image pick-up device shown in FIG. 3, a high-sensitivity pixel signal and a low-sensitivity pixel signal are alternately output from the horizontal transfer section. Therefore, it is possible to generate an image signal having a wide dynamic range. For example, in FIG. 3, output is carried out in order of “GgRrGgRrGgRr . . . GgRr” in the horizontal transfer of an initial stage and is carried out in order of “BbGgBbGgBbGg . . . BbGg” in the horizontal transfer of a next stage.
Only in the case in which a static image to be recorded is photographed, however, both the high-sensitivity pixel signal and the low-sensitivity pixel signal are required to obtain an image signal having a wide dynamic range. In the image-capturing of a dynamic image and the creation of an image for the view finder display of a camera, generally, only the high-sensitivity pixel signal is enough. Accordingly, it is necessary to carry out a useless processing, for example, the separation of the low-sensitivity pixel signal and the high-sensitivity pixel signal which are alternately output. Consequently, a processing time is increased. Moreover, an unnecessary signal charge is transferred so that an increase in power consumption cannot be ignored.
The signal charge is dividedly read twice for the high-sensitivity pixel signal and the low-sensitivity pixel signal. In the case in which the low-sensitivity pixel signal is not required, it can also be omitted. In the case in which the low-sensitivity pixel signal is required, the reading operation is dividedly carried out twice even if a one-time reading operation is originally enough. Consequently, the processing time is increased. There has also been proposed a solid-state image pick-up device described in JP-A-2001-8104 in which two transfer paths for a high-sensitivity pixel and a low-sensitivity pixel are provided in a horizontal transfer section. However, the number of peripheral elements such as an AD converter is increased, and furthermore, an increase in power consumption cannot be avoided.
Moreover, it is necessary to maintain a region in which a vertical transfer section is to be formed depending on an amount of charge transfer which is supposed. In the case in which the arrangement shown in FIG. 3 is employed, a region to which the detected charge of the low-sensitivity pixel is to be transferred also occupies the same region as that for the high-sensitivity pixel. For this reason, an unnecessary region is to be maintained so that an increase in the density of an image pick-up device is disturbed.